In order to prevent shearing stress, it is known within the field of horology to use arbours that have a polygonal, i.e., non circular section so as to drive in rotation a part whose arbour hole has a shape that matches the polygonal section. However, this configuration, particularly in the case of a gear train, induces asymmetry in the arbour, which is detrimental to the isochronism of the timepiece movement and requires the other gear trains, secured to the same arbour, to adopt arbour holes of the same shape.
Moreover, in the case of a composite timepiece member, i.e. one that includes two types of material, such as a gear system of the toothed wheel-pinion type, it is difficult to attach the member to a polygonal arbour without breaking it, if one of the materials includes a very restricted plastic range area, like crystalline silicon, crystalline alumina or crystalline silica.